Bruce E Logan, Evan Pugh Professor and Kappe Professor of
Environmental Engineering, Penn State, credited the idea to fellow
researcher Justine E Mink. "The idea was Justine's because she was
thinking about sensors for such things as glucose monitoring for
diabetics and she wondered if a mini microbial fuel cell could be
used," Logan said. "There is a lot of organic stuff in saliva."

Microbial fuel cells (MFC) are a bio-electrochemical system that
create energy by harnessing the power generated when bacteria break
down organic material. Logan has studied MFCs for more than ten
years and has predominantly focussed on wastewater, however his
spit-powered device requires a slightly different approach.

"By producing nearly one microwatt in power, this
saliva-powered, micro-sized MFC already generates enough power to
be directly used as an energy harvester in microelectronic
applications," claims Logan.

It is suggested by the researchers that we could soon see
ultra-low power chip-level biomedical electronics thanks to recent
breakthroughs in MFCs, with some devices possibly functioning at
sub-microwatt power outputs. The conductivity of a woman's saliva
changes five days before ovulation, which means the creation of a
very small ovulation predictor, for example, could be one of the
possible devices to come out of this recent research.

The MFC was fabricated with graphene -- a two-dimensional atomic
crystal-structured material -- as an anode for efficient current
generation, and with an air cathode for enabling the use of the
oxygen present in air, making its operation completely mobile and
free of the need for laboratory chemicals.

"We have previously avoided using air cathodes in these systems
to avoid oxygen contamination with closely spaced electrodes," said
Logan. "However, these micro cells operate at micron distances
between the electrodes. We don't fully understand why, but bottom
line, they worked."

The mini microbial fuel cell was tested using acetate and human
saliva, but any liquid with enough organic material could be just
as effective. Ultimately, these findings open the door to
saliva-powered applications of this fuel cell technology for
lab-on-a-chip devices or portable point-of-care diagnostic devices,
such as the ovulation device.